This application is based on Japanese Patent Application No. 2000-188276 filed on Jun. 22, 2000 and No. 2000-203693 filed on Jul. 5, 2000 the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a rotary electric machine for a vehicle.
2. Description of Related Art
JP-A-63-87137(U.S. Pat. No. 4,825,139) discloses a rotary electric machine for a vehicle. The machine has a full bridge circuit that has MOS transistors. The MOS transistor can act as either a switch or a diode. Therefore, when the MOS transistors are turned off, they act as a rectifier bridge connection forming a diode rectifier. When the MOS transistors are turned on, they act as a short circuit connection. This machine induces a charging current even at a low rotational speed by alternating the short circuit connection and the bridge connection by rapidly turning the MOS transistors on and off. When the machine acts as a motor, a driving current from an outside source is supplied to the stator winding to provide a rotating magnetic field by controlling the MOS transistors. FIG. 13 and FIG. 14 of that patent disclose an embodiment which controls two groups of opposed phases in a complementary manner.
The rotary electric machine disclosed in JP-A-63-87137 generates audible noise because a magnetic field in the stator core is changed at a high-frequency. Further, such high-frequency noise is very harsh and loud relative to other noises from other rotary machines and the engine at a low rotational speed range.
Further, the rotary electric machine disclosed in JP-A-63-87137 can not supply a plurality of voltages.
The present invention addresses these drawbacks by providing an improved rotary electric machine for a vehicle.
According to a first aspect of the present invention, a rotary electric machine has two sub-windings shifted by a predetermined electric angle. The rotary electric machine has bridges connected to the sub-windings. At least one of the bridges is interchangeable between a rectifier bridge connection and a short circuit connection in response to a high-frequency switching control by a controller. Therefore, audible noise can be reduced by canceling major components of magnetic forces generated by the sub-windings, and a current can be supplied from a low rotational speed.
According to a second aspect of the present invention, two bridges are interchangeable between two connection states. The second bridge is in a substantially opposite connection state to the first bridge. The second bridge is in the rectifier bridge connection when the first bridge is in the short circuit connection. The second bridge is in the short circuit connection when the first bridge is in the rectifier bridge connection. Therefore, audible noise generated by a high-frequency switching operation can be decreased by canceling magnetic forces of the first and second sub-windings.
According to a third aspect of the present invention, a rotary electric machine has two sub-windings which have individual output terminals. The rotary electric machine has switches connected to at least one of the sub-windings for switching between a short circuit connection and a rectifier bridge connection. Therefore, two voltages can be supplied from the sub-windings, and a current can be induced in at least one of the sub-windings even from a low rotational speed.